Commercially available microCT (computed tomography) systems have failed to meet the challenging demands for small animal imaging, beyond the single requirement for good spatial resolution. Specifically, they have failed to take into account that the thousand times smaller volume in mice, compared to humans, is also coupled with ten times faster heart rates, and increased respiratory rates and circulation times. Thus, the currently available systems have been limited to either: (1) in-vivo volume CT, which is primarily useful for co-registration of anatomical and with functional images provided by positron emission tomography (PET) or single photon emission computer tomography (SPECT); or (2) ex-vivo high spatial resolution CT, with sufficient contrast resolution for specimen imaging. However, these commercial systems have all failed to address the significant pre-clinical applications for micro-CT, which require improved tissue contrast, lower dose, and faster acquisition times to allow for dynamic images acquired in small animals and to take full advantage of the use of contrast agents. The goal of this project is to develop a next generation microCT for pre-clinical imaging for drug development and medical research. The system will be designed to provide clinical quality CT images in vivo in mice and rats, with performance specifications optimized to accommodate the demanding requirements of the most critical areas of current medical research. Specifically, the instrument will provide very good spatial resolution, ultra fast frame speeds (< 1 second), and low radiation dose to the subject. This will be achieved utilizing a photon counting mode for x-ray acquisition, instead of the standard current integration mode. The system will be capable of gross energy information and energy binning, and thus will provide "Color-CT(tm)" capability, allowing tissue compositional analysis. To accomplish these advances, the system will feature advanced CdTe solid state detectors, coupled to high speed integrated circuits for signal processing, to achieve performance characteristics not currently possible from conventional technologies used by the major CT manufacturers. In Phase-II, a fast dynamic multi-slice Color-CTTM scanner prototype will be developed, employing multiple detector modules in a novel system design incorporating a very fast x-ray source. This new modality, once established in the microCT marketplace, will undoubtedly translate into human CT scanners, and given the current study volumes of clinical CT, the impact that this project imparts to the field of medical imaging will indeed be dramatic. [unreadable] [unreadable] [unreadable]